- 學位論文
特高壓地下環路供電系統與用戶主變壓器低頻諧振之研究
A study on the Low Frequency Resonance of VHV Underground System with Loop Structure and Main Transformer of Consumers
摘要
特高壓地下供電系統包括電力公司及用戶，變電所內之主變壓器、匯流排及開關操作介於主變電所內之特高壓電纜，當電力公司因為人為或天然等災害導致停電時，特高壓地下環路供電之用戶主變壓器一次側電源端是未切離的狀態，此目的是為了減少特高壓開關操作的次數以減少受開關突波的衝擊，延長特高壓開關的壽命，這使得地下電纜的等效容與變壓器激磁電感在系統上發生並聯而誘發諧振，因電纜電容很大諧振頻率可能低於系統頻率，此種低頻諧振對變壓器及比壓器等都有不利的影響，有鑑於此，本論文以典型特高壓(161kV)之地下環路供電系統為對象探討其用戶端在諧振時之相電壓及諧振電流，考慮各用戶主變壓器開關不同的切離操作下所造成地下供電環路之諧振影響。文中首先以電磁暫態模型分析程式(EMTP/ATP)建構模型，然後分析前述各種狀況下各用戶端電壓與主變壓器電流之諧振情形及最終之殘餘電壓，最後據此評估其影響，其中將分析地下環路供電系統因電力公司停電可能因低頻諧振及殘餘電壓造成用戶主變壓器與比壓器(PT)損壞及電纜本身可能的傷害，研究結果顯示低頻諧振可能使主變壓器及比壓器的鐵芯飽和，而造成長時間的過激磁電流使其受損，至於電力公司電源端三相不同時切離可造成過高的殘餘電壓使GIS各設備及電纜接有過壓之情形，尤其當電源再度投入時造成背對背加壓，對電纜瞬間極大的衝擊，必須加以防範。本研究分析結果可供擬定防範措施之參考。
並列摘要
The very high voltage (VHV) underground distribution system comprises of main transformers, and VHV underground cables among these substations. If the utility outage with open the circuit breakers and switches off the sources of underground cables, most of customers only open their main breakers of main transformers at secondary without open their primary breakers thus the transforms are still connected with cables. So, the resonance between cable capacitance and transformer excitation inductance may be induced. The reason ant frequency is usually lower than the system frequency which has detrimental effects on main transformers and other voltage and current transformers. For this, this thesis is to study the low frequency phenomenon for VHV (161kV) underground distribution system with loop structure, in witch the resonant voltages and currents are investigate with respect to various switching schemes. The circuit models is first constructed by using the electromagnetic transients program/alternative transients program (EMTP/ATP). Then, the resonant voltages and currents and residual potential at customer main transformers are analyzed. Based on these analysis results, the affections on customer main transformers, and voltage transformers (VT) are evaluated. The study results had showed that over exciation currents will occurrence on main transformers and VT during low frequency resonant and very high residual voltages may arrised due to non-synchronous operation among poles of breaker (or switch). This very high residual voltage may lead to insulation failure on main transformer switchgears, VT and any equipments connected with the cables, even have tremendous impacts when cables are back -to- back re-energized. All the informations of this study are beneficial for further studies on related subjects.